1. Field of the Invention This invention relates to the process and apparatus for making prosthetic suction liners and coating tubular substrates.
2. Background of the Invention
Prosthetic suction liners have been described in U.S. Pat. No. 4,923,474 granted to Klasson and Kristinsson on May 8, 1990; U.S. Pat. No. 5,728,168 granted Mar. 17, 1998 to Laghi et al.; and U.S. Pat. No. 5,830,237 granted to Kania Nov. 3, 1998.
The original suction liner as described in U.S. Pat. No. 4,923,474 was formed of a silicone elastomer and was adapted to the rolled over residual limb of a prosthetic user in a manner fully described in the patent.
The manufacturing process for making suction liners with a fabric exterior covering adhered to one or more cured elastomer inner layers typically involves multiple injection molding procedures and possibly laminating procedures that are designed to build-up the various layers constituting the suction liner. Obtaining an intimate bond between the silicone and fabric layers is particularly important, particularly when it is necessary to maintain full elasticity of the suction liner to enable it to closely fit over and conform to a residual limb of a prosthetic user.
The process is more complicated when a distal prosthetic connector fitting must be incorporated in the distal end of the suction liner, particularly when an injection molding procedure is utilized.
Injection molding procedures are time consuming and require complex equipment to ensure accurate shapes and thicknesses of various size suction liners. Injection molding thick, soft elastomeric layers on the inner surfaces of suction liners also present a challenge using injection molding techniques.
Prior art procedures for continuously coating tubular substrates with a cured elastomer coating or film involve many different procedures that tend to be expensive and time consuming. It is highly desirable to continuously coat tubular substrates with an elastomer layer intimately bonded or adhered to the substrate in a convenient, low cost procedure, particularly where the substrate is an elasticized, porous fabric.
The invention relates to a process for forming a generally conical, close ended suction liner having a fabric outer covering, a thin cured silicone elastomer coating preferably provided on the interior surface of the fabric and a cured silicone elastomer lining adjacent the intermediate silicone coating. The prosthetic suction liner is formed with a distal end cap in which a prosthetic xe2x80x9cumbrellaxe2x80x9d connector is embedded at the distal end of the suction liner using a process according to the invention described herein. The prosthetic connector is exposed in a central portion to provide access to a prosthetic pin connector in a conventional manner. An optional reinforcement layer may be embedded in the innermost silicone elastomer layer using the inventive process to restrict axial elongation of the distal end portion of the suction liner while permitting lateral distension of the liner material in that portion of the liner in which the reinforcement material is embedded in the silicone elastomer layer.
One aspect of the inventive process involves providing a cylindrical tubular length of elasticized fabric that is stretchable both longitudinally and laterally relative to the axis of the tube; coating the inner surface of the fabric tube with a continuous, thin cured silicone elastomer that partially penetrates and adheres strongly to the fabric but does not extend through the full fabric thickness; optionally attaching a tubular length of reinforcement matrix material to one end of the coated tubular fabric; placing the tubular length of fabric and the optional reinforcement in a molding device; placing the umbrella prosthetic connector element in the molding device; molding and curing a silicone elastomer distal end cap over one end of the tubular length of coated fabric and the optional reinforcement matrix so as to embed the umbrella prosthetic connector in the distal end cap silicone material while bonding the distal end cap to the end of the tubular length of fabric and the optional reinforcement matrix; removing the tubular length of fabric with the molded distal end cap from the molding device and inserting a premeasured quantity of uncured silicone resin that will form an inner layer of the liner into the closed end of the fabric tube and end cap; inserting the fabric tube with the premeasured quantity of uncured resin and the distal end cap into a female mold cavity having a defined peripheral contour corresponding to a desired outer peripheral contour of the prosthetic suction liner; advancing a male mold member having an external contour corresponding to the desired inner contour of the suction liner into the interior of the tubular fabric and distal end cap assembly from its open end to cold forge the uncured silicone elastomer over the full length of a cavity defined between the male and female molds to fully form the innermost silicone elastomer layer to a desired contour and thickness and carrying out a preliminary cure of the inner most silicone elastomer in the forging device; removing the formed assembly of tubular fabric and partially cured silicone elastomer layer from the forming device and fully curing the innermost silicone elastomer layer.
Apparatus for carrying out the process includes a continuous film casting device configured to continuously cast an uncured elastomer film coating on a tubular substrate using sub-atmospheric suction to draw the film to the surface of the fabric substrate; and a heater in series with the continuous film casting apparatus arranged to cure the cast elastomer film continuously during the coating process to thereby produce a continuous tubular length of substrate coated on one surface thereof with a cured elastomer film.
When the apparatus is used to apply an elastomer coating to a porous material such as an elasticized fabric, the suction applied during casting of the uncured elastomer film is adjusted so that the film partially embeds itself in the intersices or pores of the fabric while avoiding complete penetration of the elastomer throughout the fabric thickness. This leaves the opposed surface of the fabric free of elastomer while producing a continuous sealing film of elastomer on the first surface of the tubular length of fabric.
During curing, the tension applied to the coated substrate is adjusted to produce optimum qualities for the coated length of substrate that are appropriate for the thus produced product or any subsequent use of the coated substrate in a manufacturing procedure in which the coated substrate is formed into an end product.
The thus coated tubular length of substrate may be reversed with the cured elastomer coating on the inside of the substrate. The tubular coated substrate may then be cut to lengths corresponding approximately to individual lengths of products to be made with the coated lengths of substrate and a tubular matrix of reinforcement material may be attached to one end of the end of the tubular length of substrate for use, for example, in a prosthetic suction liner.
As described previously, a distal end cap may be molded to the one end of a tubular length of coated elasticized fabric substrate with a prosthetic connector fitting or umbrella embedded in the distal end cap.
In a specific example wherein it is desired to use such a continuous coated tubular substrate in a process for making a prosthetic suction liner, the substrate comprises a tubular elasticized fabric such as circular knit fabric that is distensible both lengthwise and widthwise and the elastomer is constituted of a silicone elastomer formulated so that it may be cast as a continuous film in its uncured condition in a temperature range that is practical. The coated fabric maintains its elasticity due to the elasticity of the silicone elastomer in its cured condition. The surface of the cured silicone film may be left in a somewhat tacky condition so as to be readily bondable to a subsequent silicone elastomer layer.
The cold forging apparatus includes a female die that preferably includes suction devices to draw the fabric tube into intimate contact with the interior walls of the female die prior to the advancement of the male member into the female die. The male die member formed in accordance with a desired inner profile of the innermost silicone elastomer layer of the suction liner, is advanced into the uncured silicone elastomer previously deposited into the closed end of the fabric and distal end cap assembly so the elastomer is forced to flow longitudinally through a cavity that is formed between the female die and the male die member from the closed end of the suction liner to the proximal open end thereof. The procedure may be referred to as a cold forging process for convenience.
The rate of advancement of the male die member is controlled to permit complete flow of the uncured silicone elastomer throughout the cavity provided between the male and female die members, particularly when the gap between the male and female die members varies along the length of the molding device.
A guide pin may be inserted into the prosthetic connector element embedded in the distal end cap of the pre-formed tubular length of coated fabric, distal end cap and prosthetic connector. The female die includes an aperture at its distal end arranged to receive the guide pin to thereby center and locate the length of coated fabric and distal end cap in the female die before the male die member is advanced into the female die to cold forge the uncured silicone elastomer resin into the die cavity between the male and female die members.
The male and female dies may be heated to perform a preliminary curing of the silicone elastomer of the silicone elastomer in the mold cavity before the laminated assembly of elasticized fabric, thin coating of silicone elastomer and final inner layer of silicone elastomer are removed from the die.
The process and apparatus constituting the inventive subject matter will be described in more detail in the drawings and description that follow.